Monolith-type membrane structures using a porous support having an array of parallel channels, typically in a cylindrical form, and a gas selective membrane coated on the inner surface of channel walls, offer a higher surface area packing density than a single-channel tube of the same diameter, leading to higher permeation flux. This results in a dramatic reduction of both the membrane cost per surface area and the engineering costs to assemble large surface areas of membrane modules. The structures can be used to solve significant energy and environmental problems; for example, H2 recovery from waste gas streams, H2 purification from a production gas mixture for fuel cells application, CO2 capture from flue gas streams for sequestration, and other separations. These separation applications often require high temperature for better separation performance.
When a mixture gas stream to be separated is supplied into the channels of a monolith ceramic membrane product, it is separated through the membranes coated on the channel walls, and the permeate thereafter passes through pores of the membranes and pores of the support to flow out to an external space. The surface area of two ends of the support exposed to the stream, which includes the end flat surface, and the exterior curved surface of the support, have no membrane coating and therefore need to be sealed with a sealing material in order to prevent the gas stream being treated from entering and passing through the exposed end surface area and then passing through the pores of the support and flowing out of the support with no separation occurring. The separation function is therefore more efficient with a seal coating on the end portion of the support. For separation to occur it is necessary for the gas stream to enter the open area of the channels and flow through the membrane coated channel walls and the outer porous wall of the support.
There is a need for hermetic sealing of the exterior surfaces of an alumina membrane support structure to prevent gases from entering or exiting the support through the exterior surfaces instead of entering the open area of the channels, passing through the membrane coated channel walls and exiting through the unsealed walls of the support.